Cannabis use can lead to suicidal thoughts

Globally, suicide has emerged as the second leading cause of death among youth aged 10-24 years old. The World Health Organization estimates that in the year 2000, around 1 million people died from suicide. On average, there are three male suicides worldwide for every female suicide.

There continues to be much debate as to the role cannabis use may play in the rise of youth suicide. Although use has declined in recent years, cannabis continues to be the most popular illicit drug amongst young people and stronger evidence is emerging regarding the potential negative mental health effects associated with its use.

The researchers were able to identify that regular cannabis use is indeed a risk factor for suicidal ideation for males and that it is not suicidal ideation that causes cannabis use.

A study co authored by Professor Jenny Williams in the Department of Economics sought to determine whether cannabis use plays a causal role in explaining suicidal behavior of youth using longitudinal data on a birth cohort. ‘While most users of cannabis do not suffer any significant ill effects from its consumption, there is mounting evidence that early onset of cannabis use leads to an increased risk of several adverse outcomes including cannabis dependence, early school leaving, and perhaps psychosis’ explained Professor Williams.

Understanding the underlying causes of suicidal behaviors is an important, yet understudied area in economics. Suicidal behaviors impose significant economic costs on society.

For example, the cost of completed suicides by 10-24 year olds in the US in 2005 was estimated to be $6 billion in medical expenses and lost work alone. Non-fatal suicidal behaviors have been shown to reduce the likelihood of young adult’s participation in education and employment’ highlighted Professor Williams.

This study was part of the Christchurch Health and Development Study (CHDS), which followed a cohort of children born in Christchurch, New Zealand in 1977 over 30 years.

The CHDS is uniquely suited to studying the causal relationship between non-fatal suicidal behaviors and cannabis use, containing annual information on suicidal ideation and annual information on the uptake and intensity of cannabis use for the cohort from the age of 15.

The cohort has been studied at birth, four months, one year and at annual intervals to the age of 16 years, and again at ages 18, 21, 25 and 30. Information was obtained from a variety of sources including parental interviews, teacher reports, self- reports, psychometric assessments, medical and other recorded data.

The core of the data used in this paper relates to information gathered when the respondents were aged 15-30 years. During this time, participants were interviewed up to 6 times at ages 15, 16, 18, 21, 25 and 30. This study co authored by Professor Williams was based on 938 individuals (479 females and 459 males), which represents 74% of the original birth cohort.

Previous studies have found that suicidal ideation is often more prevalent among regular cannabis users than it is among those who have never used the drug regularly. This study aimed to determine the extent to which this correlation represents a causal relationship.

The researchers were able to identify that regular cannabis use is indeed a risk factor for suicidal ideation for males and that it is not suicidal ideation that causes cannabis use.

‘Regular cannabis use is estimated to increase the hazard of transitioning into suicidal thoughts for males but not females. Further investigation reveals that that the effect for males is driven by those using at least several times per week. Finally, we find no significant effect of suicidal ideation on the uptake of regular cannabis, for either males or females, once the endogeneity of suicidal ideation is accounted for’ observed Professor Williams.

This research aims to shed light on the links between cannabis use and suicidal behavior as Professor Williams explained, ‘our research provides new evidence that intensive cannabis use that starts at a young age increases the rate at which susceptible young people start having suicidal thoughts’.

‘This is of significant policy interest since it provides clear information for the targeting of youth suicide prevention programs, identifying behaviors and ages that produce large increases in the risk of transitioning into suicidal behavior. Our paper provides credible evidence that the early onset of suicidal ideation is a further adverse outcome of youthful cannabis use for these vulnerable individuals’ outlined Professor Williams.

This research was presented at the 2nd National Cannabis Conference, held in Brisbane from 19-21 September 2012.